Plastic bags of various types are in widespread use throughout the world. Such bags can be economically manufactured in large quantities from extruded plastic films, and a variety of machines have been developed for automating the bag-making process. Advancements in such machines facilitate high speed, economical manufacture of such bags.
Plastic bags are typically formed from a continuous plastic web that can be in the form of a flattened continuous tube or a continuous folded sheet. By forming bottom welds, in the case of a tubular web, and side welds, in the case of a folded web, individual bags are defined. Typically, a perforation adjacent the bottom or side weld allows separation of the individual bags. Until separation, the bags remain strung together in a continuous ribbon.
For eventual use of the bags, it is frequently desirable that the bags be separated from one another for packaging. At the same time, relatively large bags must ordinarily be folded in order to economically and conveniently package the bags. To this end, integrated machinery for effecting separation and folding of such plastic bags has been developed. U.S. Pat. No. 5,388,746, hereby incorporated by reference, illustrates one such separator/folder machine which has proven to greatly facilitate high-speed manufacture and packaging of bags.
In an apparatus which is disclosed in the above-referenced patent, individual bags are separated from each other, and subjected to a sequential folding process. In particular, an intermediate portion of each bag is directed between a pair of cooperating nip rollers, and associated flat belts, which effect formation of a fold in the bag across its width. By successive formation of such folds (for example, three), the length of the bag can be reduced to one-eighth its original length. In conjunction with longitudinal folding of the bag, typically effected prior to transverse folding, relatively large bags can be conveniently packaged for eventual use by consumers and other end users.
Use of relatively lightweight, light gauge plastic film materials for bag manufacture is desirable to facilitate economical manufacture. However, experience has shown that use of an apparatus such as disclosed in the above-referenced patent with relatively light gauge plastic film materials, at the high speeds at which such an apparatus is capable of operating, can result in undesirable wrinkling, folding, buckling, or like undesired variations from the desired folding sequence. Such undesired effects can result from the manner in which portions of the bags must be subjected to a sudden change in direction of movement attendant to the folding sequence. Additionally, the relatively lightweight bag material can exhibit a lamination-like adhesion to the relatively wide, flat belt and associated rollers which are employed in the folding mechanisms of the apparatus disclosed in the above-referenced patent.
Accordingly, the present invention contemplates specific features which can be incorporated in a bag-making apparatus of the above type for facilitating high-speed handling and folding of plastic bags, and particularly those made from relatively lightweight, light gauge plastic film materials.